Changes in protein expression across developmental time were used to cluster protein spots into six groups (c0-c5). Each group contained protein spots whose expression peaked at a particular developmental age. In each panel the y-axis represents relative expression levels and the x-axis represents the ages analyzed. Black dots represent ages E13, E15, E17, E18, P0 and P5 from left to right respectively. Protein spots whose expression peaked at E17 (c1), P0 (c4) and P5 (c0) were picked for identification. Gray lines represent one standard deviation on either side of the mean expression pattern for each group of proteins.